[PATCH v13 5/9] nvme: add copy offload support

[Christoph Hellwig]

> +	if (blk_rq_nr_phys_segments(req) != 2)
> +		return BLK_STS_IOERR;

The magic number of segments adding up source and dest really need
constants and helpers to make the code understandable.

> +	/* +1 shift as dst+src length is added in request merging, we send copy
> +	 * for half the length.
> +	 */
> +	n_lba = blk_rq_bytes(req) >> (ns->lba_shift + 1);

I do not understand the logic and comment here.

> +	if (WARN_ON(!n_lba))

WARN_ON_ONCE

> +		return BLK_STS_NOTSUPP;

and BLK_STS_NOTSUPP seems like the wrong error here, this is an
invalid argument.